Software that can track a computer user's every move (known as "spyware" and "adware") is finding its way into more PCs - unsolicited. Some programs allow advertisers to find the precise type of customer they want and then send a targeted pop-up ad.
A similar practice of precision marketing has been done for decades via the telephone and mail. But the difference with the Internet is a higher level of personal information that's gathered with every website visited.
Google, the premier search engine on the Web, has even set up a free e-mail service that tracks key words in a person's e-mail and then pops up a related ad.
Spyware is installed invisibly on a computer when an individual shares a file, downloads free or paid software programs, or visits certain websites. It can be used to create "backdoors" into a person's computer, allowing third parties to steal personal information.
It also uses up computer power, can crash machines, and create a blizzard of unwanted ads.
Last week, one Internet service provider teamed up with a maker of anti-spyware to audit some 1 million computers. It found 29.5 million pieces of spyware - or 28 per computer.
Some computer-focused organizations, like the Center for Democracy and Technology in Washington, are working to increase public awareness of spyware and its risks. One conclusion - users must pay closer attention to the details in licensing agreements that pop up on the screen before clicking "OK" to downloading documents, or anything else. Often, those agreements legally allow the addition of spy- or adware to the user's computer.
Legislation in Congress rightly aims to keep spyware from being installed without user notice and consent. States, too, are considering similar action.
This week, the Federal Trade Commission spent a day focusing on the problem, weighing possible regulation. But the first line of defense lies with the individual user who can develop the skills or buy the help to keep spyware out in the cold.